where can i find simple explanation of how they distinguish elastic vs inelastic collisions? They talk about the ratio of elastic vs inelastic collisions as a f

where can i find simple explanation of how they distinguish elastic vs inelastic collisions? They talk about the ratio of elastic vs inelastic collisions as a function of incident particle energy which is where I am confused. Excuse my ignorance - I am interested though not schooled in the particulars of particle physics. They also talk about cross section - I imagine they calculate that based on the frequency of collisions - just like Rutherford did.